The present invention relates generally to systems, apparatuses and processes associated with the fluid catalytic cracking (FCC) process used in petroleum refineries. More particularly, the invention relates to systems, apparatuses and processes for removing catalyst, catalyst fines and coke particulates typically found in the bottom stream or slurry oil of FCC reactors.
The FCC process is designed to thermo-catalytically upgrade the yield and quality of higher boiling point, distillate, intermediate products provided by the crude atmospheric and vacuum fractionators located upstream in the crude oil refining process. Of all the refinery processes, the FCC process has one of the highest operating costs and is one of the most difficult to operate reliably for extended periods of time. This process is also the primary source of high quality olefans and isobutene for alkylation into a low sulfur and high octane gasoline stream. Therefore, the FCC process is an important process in crude oil refining.
Since the introduction of the FCC process in the 1930s and 40s, the process has undergone a number of changes and upgrades. Those changes and upgrades have focused on catalyst formation, process design, process control, refractory formulation and installation, metallurgy, power recovery, air emissions control, and process availability or uptime. The industry is still searching for ways to improve performance, reduce operating costs, and increase uptime throughout the FCC process.
Every two years, the National Petrochemical & Refiners Association holds a two-day question-and-answer seminar focused strictly on improving the FCC process. At every session there are always questions focused on the removal of catalyst, catalyst fines and coke particulates from slurry oil. To date no long term, cost effective and operationally viable solutions have been found. This is particularly true when it comes to dealing with FCC fractionator slurry oil and the operational problems created when it becomes contaminated.
FCC fractionator slurry oil becomes contaminated with catalyst, catalyst fines and coke particles at levels ranging from less than 0.25% to greater than 2% as carryover from the hydrocarbon vapor entering the fractionator. Contaminant particle size can range from 1 micron (fines) to 90 microns (catalyst). This contamination occurs naturally at very low levels with undamaged and properly designed riser termination and primary and secondary cyclones in the FCC reactor. During an upset in the reactor, or as the FCC reactor is reaching the end of its planned run length, loss rates of catalyst and fines, along with coke fine generation, can increase to much higher levels, thereby affecting operational control of the FCC process. Poorly operating reactor cyclones can result in elevated levels of fresh or equilibrium catalyst loss to slurry oil in the range of 3 to 5 tons per day over the typical 1 to 3 tons per day normally seen.
Catalyst and fines contamination, especially when it occurs for extended periods of time, causes one or more of the following undesirable effects:                1. Increased metallurgical loss rates due to erosion in the slurry oil loop affecting heat exchangers, steam generators, control valves, pumps, and process lines.        2. Increased fouling and plugging of slurry oil loop fractionators, heat exchangers and steam generators, as well as high pressure drops.        3. Increased fouling of slurry oil decant and storage tank bottoms while settling catalyst from slurry oil to meter intermediate or product ash content specifications.        4. Increased operational cost to repair the damaged or fouled equipment.        5. Increased operational costs to clean and dispose of Resource Conservation and Recovery Act (RCRA) hazardous oil wet solids in the bottom of slurry oil storage tanks.        6. Increased operating difficulty in meeting optimum unit performance.Next to the cost of the catalyst itself, dealing with the above issues can become the second highest operating cost in the FCC process. As the severity of contamination increases, it becomes a major limiting factor to meeting run-length expectations while maintaining optimum product conversion and yield.        
Currently there are no technologies that can recover catalyst, catalyst fines and coke particles from a FCC fractionator slurry oil loop because of temperature, pressure and size limitations. Filtration technology has been designed and applied in the lower temperature slurry oil being sent to storage. Several manufacturers have sold a limited number of these filtration units over the last 10 to 15 years, but few if any of these units are operational today. Although the units meet expectations in terms of removal efficiency, the capital and operating costs are prohibitively high and operational control proves difficult and complex. Additionally, inventorying, cleaning and replacing filters is labor-intensive and complicated, redundant filter housings are required, and the filters have to be backwashed frequently. Therefore, a need exists for a cost-effective and efficient method for removing particulates from slurry oil.